The overall goal of this project is to provide non-invasive in vivo determination of fiber tracts using diffusion tensor imaging (DTI) tractography to aid neurosurgeons in sparing eloquent regions during brain tumor resection and biopsy. DTI tractography is the only technique that can non-invasively predict the locations of subcortical fiber tracts. While there is much a priori knowledge about the general location of specific neurons and their axonal projections, the variability between individuals makes it impossible to know these locations precisely without further study. Furthermore, in the presence of neoplasm these tracts can be diverted from their normal trajectory or damaged. For DTI tractography to be used to determine white matter tracts, a starting region that is part of the tract must first be identified. Techniques that can specify the cortical location of specific function related neurons are magnetic source imaging, functional magnetic resonance imaging and intraoperative mapping by cortical stimulation. Intraoperative stimulation mapping is the gold standard for determination of functional areas but both MSI and fMRI have been shown to have some utility in predicting these areas pre-surgery. While DTI tractography can provide subcortical tracts, the lack of specific starting points to generate these tracts is a weakness of this technique in the absence of specific a priori knowledge of the tract location. Therefore, DTI tractography and intraoperative mapping are complementary techniques and the combination of these techniques may both serve to validate the DTI tractography method and lead to improved characterization of eloquent regions during neurosurgery.